The goal of this project is to investigate the phonological systems of prelingually profoundly deafened children after long- term use of cochlear implants. Previous research has demonstrated that cochlear implants can be an effective device for promoting both speech perception and speech production in children with profound hearing impairment. However, because of the relatively recent introduction of cochlear implants as a treatment option for pediatric patients, speech production has not been assessed much beyond three years of device use. Using methods and techniques from clinical linguistics, the proposed project will provide detailed information regarding the phonological knowledge and underlying linguistic systems of ten children who have used cochlear implants for a much longer time, at least five years. The proposed project will therefore provide for the first time detailed information about the phonological systems that long-term users of cochlear implants actually develop, information about the differences between these systems and the target system, and information about directions of development and change in these systems. Data from this study will provide important new knowledge regarding the way in which language can develop using a type of auditory input (electrical stimulation) that is unique in the history of humankind. Specifically, it will provide new information about how this type of auditory input can facilitate the development of phonological systems similar to target phonological systems.